Suppose a quantum version of gravity exists (which I don´t think). What will be the quantities in the uncertainty relation connected with this quantum gravity? Some time ago I sent a letter to Lee Smolin after which of course no answer came. But later I saw in an article that in his version (LQG) volume and area of space were the two quantities. Is this the case in all suggested types of quantized gravity?

  • 2
    $\begingroup$ "Suppose such a theory exists. What would it look like?" how could anyone know? $\endgroup$ – AccidentalFourierTransform Apr 2 '16 at 14:58
  • $\begingroup$ Be the first one to make a measurement that finds a quantization of spacetime and we will all be smarter... rest assured, if you do, Smolin will answer your mail. :-) $\endgroup$ – CuriousOne Apr 2 '16 at 15:01
  • $\begingroup$ @Curiousone Haha! :-) There still isn´t a quantum theory of gravity. And I think it´s not so that who does a measurement and finds a quantization of space-time (a measurement wich seems to me almost impossible) first is the smarter (and gets a lot of letters from Smolin, unless his theory wasn´t the right one). That doesn't rule out the possibility of fantasizing about the two quantities what the quantities are of the uncertainty relation of a specific theory. They´re not gonna be E and t and x and p, that´s for sure. These are the quantities for particles moving through space. $\endgroup$ – descheleschilder Apr 2 '16 at 20:21
  • $\begingroup$ No measurements, no physics... just phantasies. Mother nature is a woman, after all... if she doesn't want to be your girlfriend, then all you have are your dreams about her... $\endgroup$ – CuriousOne Apr 2 '16 at 21:16
  • $\begingroup$ But if she is my girlfriend, wich she is, I can fantasise about her and at the same time look what she is doing, touch her, smell her and listen to her. And maybe she doesn´t want to be your girlfriend if you measure her to deep. You must allow a good friend to have her secrets, and not want to know every little detail of her. Just having fantasies will suffice, wich will be in fact a good thing to maintain the relationship. Besides, how can you, in physics, make a measurement without having fantasised before what you are going to measure? Fantasy and measurement go hand in hand. $\endgroup$ – descheleschilder Apr 3 '16 at 15:22

Models based on string theory have consistent quantization of gravity. Within these , there is theoretical work carried out for generalizing the uncertainty principle for quantum gravity.

One example :


It generalizes the usual space momentum uncertainty,(formula 15)

and another


This one examines an uncertainty in space time, formula 2.2.

It is part of ongoing theoretical research.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.